A PTFE substrate measuring 5 cm x 5 cm x 4.19 mm (165 mils) thick and containing drilled through holes having 457.2 mu m (18 mils) diameter or an aspect ratio of 9.16-to-1 is exposed to the reducing bath for 10 minutes with constant agitation of the substrate to promote solution flow through the vias.
Furthermore, these "dry processes" have the potential advantage of greater process control and higher aspect ratio images.